Modulation



T. H. PRICE Sept. 10, 1935.

MODULAT ION Filed June 9,

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Patented Sept. 10, 1935 UNITED STAT FFICE MODULATION Application June 9, 1933, Serial No. 674,984 In Great Britain June 20, 1932 2 Claims.

This invention relates to modulation systems for use in radio and other modulated carrier frequency signalling systems and has for its object jto provide an improved and eiicient modulation system capable of dealing satisfactorily with a wide range of modulating frequencies.

The invention is applicable broadly to all known systems wherein modulation is effected by varying anode voltage.

According to this invention a modulation System comprises a pair of high frequency valves connected in phase opposition, a tuned oscillatory output circuit coupled between the anodes of said valves, and means for applying modulating potentials as part of the anode potentials applied to the phase opposed high frequency valves.

The invention is illustrated in the accompanying diagrammatic drawing, in which:

Figure 1 shows a circuit including the modulation scheme of the present invention; while,

Figure 2 shows a modification of the circuit of Figure 1.

Referring to Figure 1, which shows one way of carrying out the present invention as applied to a so-called parallel choke modulation system, the valves V1, V2, which may operate at high frequency, have their cathodes l, 2 connected together and their anodes 3, 4 coupled together through a tuned oscillatory output circuit consisting of inductance 5 and capacity 6 in parallel, the opposite ends of this tuned circuit being coupled each through a condenser 'l or 8 to the anode 3 or l of one of the high frequency valves. The high frequency oscillations may be produced in these tubes or supplied thereto from a separate source. The anode of each high frequency valve is also connected through a high frequency choke 9 or lil to the anode Il of a modulation valve V3, to Whose grid circuit the modulating potentials are applied, the anode of said modulating valve being connected through the usual low frequency choke I2 to the positive terminal +HT of a source of anode potential. The negative terminal HT of this source is connected to the common cathode point of the three valves.

In a modified arrangement in accordance with the present invention and shown in Figure 2, and wherein the invention is applied to a so-called series modulation system, the anodes 3, 4 of the two high frequency valves V1, V2 are coupled together through a tuned circuit 5, and coupling condensers l, 8 as in the last described embodiment, each anode being also connected 5 through a high frequency choke 9 or i0 to the positive terminal |IIT of a source of anode potential, this source being shunted by a condenser I3. The anode cathode space of the modulating valve V3 is connected in series with a further 10 high frequency choke lll between the negative terminal -HT of the source and the common cathode point of the high frequency valves, the modulating potentials being applied to the grid circuit of the modulating valve Vs.

It will be seen that both the modulation circuits described present the advantages that Ithey are simple and easy to construct, inherently balanced, and well adapted to give satisfactory and eicient modulation over a Wide range of modulating frequencies since the anode cathode space of the high frequency valves are not shunted by the oscillatory output circuit while furthermore the coupling condensers by which the said oscillatory output circuit is coupled to the anodes of the high frequency valves may be made quite large without disadvantageous effects due to shunting away of the higher modulating frequencies.

Having thus described my invention and the operation thereof, what I claim is:

l. A modulating device comprising a pair of thermionic tubes each having anode, cathode and control grid electrodes, means for applying carrier wave oscillations to be modulated to the control grids of said tubes, a tuned circuit connected between the anodes of said tubes, a blocking condenser interposed in said connection between the anode of each tube and said tuned circuit, an additional thermionic tube having a control grid electrode energized by signal potentials, said additional tube also having an anode electrode and a cathode electrode, and inductive means for connecting the anode to cathode impedance of said additional tube in series with the anode to cathode impedances of said first named tubes.

2. A modulating device comprising, a pair of thermionic tubes each having anode, cathodeand control grid electrodes, means for applying carrier Wave oscillations to be modulated to the control grids of said tubes, a tuned circuit connected connecting the anode of said additional tube to between the anodes of said tubes, a blocking conthe cathodes of said pair of tubes, means for condenser interposed in said connection between the necting the cathode of said additional tube to the anode of each tube and said tuned circuit, an adnegative terminal of a source of potential, and ditional thermionic tube having a control grid means. for connecting the anodes of said pair of 5 electrode energized by signal potentials, said adtubes to the positive terminal of said source of dtional tube also having an anode electrode and potential.

a cathode electrode, a radio frequency impedance THOMAS HENRY PRICE. 

